[sdiy] Where to buy ceramic caps

David G Dixon dixon at mail.ubc.ca
Sun Dec 31 06:38:21 CET 2017


We're both confused.  I am just having a bit of a tantrum because buying
capacitors is infinitely harder than analog circuit design.  I don't think
that's the way it should be.  I agree with you about Digikey.  I have never
actually ordered from Mouser, so I'll have to take a closer look.  I often
start by looking at Octopart to see where I should start looking (for
bargains).

Now I'm thinking that I might mix up 1n, 10n, 100n and maybe 1u caps to keep
all the resistor values between 1k and 100k (actually between 1.3k and 91k).
In that case, I'll probably use those little plastic film caps (the little
yellow or blue boxes), cuz I don't want to have any X7R or other garbage in
my circuit (too high temp coeff).  It all boils down to how close they are
to each other.  Maybe I'll go and make some more measurements...

Here's the capacitances of 10 yellow box film caps 1n0j (1nF, 5% tolerance),
in pF:

990, 997, 1001, 993, 1005, 1016, 995, 978, 1006, 994.  This is 997.5 +/-
10.3 pF.  That's about 1%.  If I remove the 1016 and the 978, then the
tolerance is only 0.6%.  This is certainly good enough for the PDN.

Hey, this is fun!  Let's try 10 blue box film 104 caps.  In nF:

102.2, 103.2, 102.4, 100.3, 100.0, 100.2, 101.7, 102.4, 101.8, 102.1.  This
is 101.6 +/- 1.1 nF.  Again, this is about 1% tolerance.  Removing the four
furthest out drops the tolerance to about 0.3%.

So, this sorting is easily done for handbuilt through-hole units (and I
will), but I'm not sure about SMD caps.


> -----Original Message-----
> From: Brian Willoughby [mailto:brianw at audiobanshee.com] 
> Sent: Saturday, December 30, 2017 6:52 PM
> To: David G. Dixon
> Cc: SDIY
> Subject: Re: [sdiy] Where to buy ceramic caps
> 
> On Dec 30, 2017, at 6:19 PM, David G Dixon <dixon at mail.ubc.ca> wrote:
> > It's not design I have a problem with -- it's procurement.  I hate 
> > buying this stuff.  Having to buy this shit from dealers 
> like Digikey 
> > and Mouser almost makes me want to find a different hobby.  
> Going on 
> > those websites with tens of thousands of options makes me want to 
> > puke, and it's why I spend so much time and money at my local shop, 
> > Lee's Electronics in Vancouver.  The only online retailer I really 
> > like is Small Bear, because there is a drag-down menu for component 
> > values.  On Digikey, the same capacitor in different values 
> is spread 
> > across dozens of pages, each with a dizzying array of 
> options, most of which I don't understand.
> 
> I'm quite confused, now. At the beginning of this thread, I 
> got the impression that you were disappointed by the lack of 
> supply options. Now it seems that you're complaining that 
> there are thousands of options. Are you saying that you'll 
> only be happy if online retailers carry exactly what you 
> think you want and nothing else?
> 
> Personally, I find Digikey to be the worse web design ever. 
> It baffles me that online electronics bloggers talk about how 
> "great" Digikey is for finding the parts they need. I guess 
> it's perhaps all due to a different way of thinking. I'm 
> open-minded enough to conceive that some people think 
> differently than I do when it comes to parts selection. It's 
> certainly something that is complex enough that my associates 
> have asked where this sort of thing is taught in the industry.
> 
> In contrast, Mouser allows me to specify exactly the details 
> that I care about, either by single values or by ranges, and 
> then drill down to a specific part by narrowing the options 
> until all that's left is to sort by price and pick the 
> cheapest. That works for me every time, and Mouser seems to 
> constantly be adding more parts that I know about, but which 
> were previously not stocked or listed by them. Mouser have 
> even improved the search engine to allow searching across 
> varying types of capacitors or resistors that were previously 
> only searchable separately. My only complaint is that their 
> price sorting doesn't take into consideration your desired 
> quantity, so I'll have to look ahead as much as a page or two 
> to find the actual lowest cost at my quantity. There's also 
> the issue that custom names are global, not per-project, but 
> that's not an issue for larger companies where parts 
> procurement is done by someone other than the circuit 
> designer or layout engineer, so I'll forgive them for not 
> catering to the really small business.
> 
> In any case, every day there are more fabrication services 
> that will handle parts procurement for you. So, if you really 
> don't like the effort that it takes for this, you can pay 
> someone else to do it for you. Advanced Circuits is one of 
> many options.
> 
> Brian Willoughby
> Sound Consulting
> 




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